1. Field of the Invention
The present invention relates to an inkjet ink, a method for producing the inkjet ink, an ink cartridge, and an inkjet recording method.
2. Description of the Related Art
An inkjet recording method is a recording method for forming an image by applying ink droplets onto a recording medium, such as plain paper or a glossy medium. As the price is reduced and the recording speed is increased, this method is rapidly spreading. In addition, as digital cameras are spreading rapidly, and the quality of images formed by the inkjet recording method becomes enhanced, it is increasingly demanded that the inkjet recording method produce recorded matter substantially equal in quality to silver halide photographs.
Also, as the size of ink droplets is reduced and the color gamut is increased by using multiple colors, the image quality can be enhanced more than ever. On the other hand, the demands on coloring materials and inks may also be increased, and demand for properties that provide high color developability and reliability, such as clogging resistance and ejection stability, may become more rigorous.
However, inkjet recording methods can have a disadvantage in that the recorded matter produced by the method can be inferior in terms of its fastness property. In general, recorded matter produced by an inkjet recording method has lower fastness than that of silver halide photographs. More specifically, the coloring material of recorded matter can be degraded by being exposed to light, humidity, heat, or environmental gas in the air for a long time. Consequently, the image is liable to deteriorate in color tone or fade.
In particular, images formed with magenta ink can exhibit the lowest fastness property of the three color inks: cyan, magenta, and yellow. Proposals have been made for dyes used in such magenta inks in order to enhance the lightfastness and the gasfastness of images.
Japanese Patent Laid-Open Nos. 8-73791 and 9-255882 propose a xanthene dye or an azo dye using H acid as a coloring material that can form images having relatively high color developability. Research has been conducted for these types of magenta dye that may be capable of producing superior color developability, and high light-fastness and gas-fastness. Also, anthrapyridone dyes are disclosed as a magenta dye producing relatively high light-fastness and gas-fastness in International Publication Nos. WO2004/104108 and WO2006/075706 and Japanese Patent Laid-Open No. 2003-192930. In particular, Japanese Patent Laid-Open No. 2003-192930 and International Application No. WO2006/075706 disclose a compound having a structure in which two anthrapyridone molecules are coupled with a linking group, and an ink containing such a compound.
Furthermore, Japanese Patent No. 3907671 discloses that an ink containing a xanthene dye or an azo dye and an anthrapyridone dye can form images superior in color developability, light-fastness, and gas-fastness. More specifically, a xanthene dye or azo dye superior in color developability, but inferior in light-fastness and gas-fastness, and an anthrapyridone dye superior in light-fastness and gas-fastness, may make a good complement to each other, and may thus produce images having high color developability and high light-fastness and gas-fastness.
As described above, various studies have been made to enhance the fastness property of images formed with magenta inks. However, no approach has yet achieved a magenta ink that adequately satisfies recent requirements for high-level color developability, light-fastness, and gas-fastness.